1. Field of the Invention
The present invention is related to a driving method and related driving device for a motor, and more particularly, to a driving method and related driving device capable of reducing production cost and preventing interference, so as to optimize operating efficiency of the motor.
2. Description of the Prior Art
Computer systems have become the most important appliances in the modern information society. With the advancement of computing rate, various circuits in a computer system, e.g. a Central Processing Unit (CPU), generate more heat under high speed operation. To dissipate the heat, the computer system can stably operate. Therefore, several heat dissipation fans are included in the computer system to lower temperatures of CPU, a graphic card, etc. Driven by a motor, a heat dissipation fan is utilized for creating airflow, so as to dissipate heat. In general, altering directions and intensity of current in a coil of a rotator of the motor, the motor can generate magnetic force with different strength and magnetic poles, to interact with permanent magnets on stators of the motor, so as to rotate the motor.
In addition to wind shear noises generated by rotation of the heat dissipation fan, high-frequency noises generated by the motor annoy users as well. Therefore, in order to decrease the noises of the motor, the prior art has developed various control methods and related control circuits to smoothly change rotating speed of the motor. Please refer to FIG. 1, which is a schematic diagram of a driving circuit 10 for a motor in the prior art. The driving circuit 10 is utilized for controlling current intensity of a coil 12 of the motor, and includes a Hall sensor 100, a pre-amplifier circuit 102, a second-stage amplifier circuit 104 and a gain determination unit 106. The Hall sensor 100 senses a magnetic pole of the rotator, transforms corresponding sensing results into differential magnetic pole sensing signals H+, H− in voltage form, and transmits the differential magnetic pole sensing signals H+, H− to the pre-amplifier circuit 102, such that the pre-amplifier circuit 102 can preliminarily amplify the differential magnetic pole sensing signals H+, H− and transmit corresponding amplifying results to the second-stage amplifier circuit 104. The second-stage amplifier circuit 104 is utilized for amplifying output signals of the pre-amplifier circuit 102 according to signals outputted from the gain determination unit 106, to output voltages OUT1, OUT2 to the coil 12, so as to drive the motor.
In detail, please continue to refer to FIG. 2, which is a time-variant schematic diagram of the differential magnetic pole sensing signals H+, H− and the voltages OUT1, OUT2 of FIG. 1. As illustrated in FIG. 2, with operations of the gain determination unit 106, when a voltage difference between the differential magnetic pole sensing signals H+ and H− is greater than 20 mv, the second-stage amplifier circuit 104 outputs the saturated voltages OUT1, OUT2, i.e. 5 V. When the difference between the differential magnetic pole sensing signals H+ and H− is smaller than 20 mv, the voltages OUT1, OUT2 outputted by the second-stage amplifier circuit 104 is proportional to the differential magnetic pole sensing signals H+, H− by a multiplier G. That is:OUT1=G×(H+−H−)OUT2=G×(H−−H+)where the multiplier G is a product of gains of the pre-amplifier circuit 102 and the second-stage amplifier circuit 104, and G=250 in this example.
Therefore, the voltages OUT1, OUT2 are gently changed, so is a slope related to the current of the coil 12 when the motor commutes, i.e. the time interval between t1 and t2 in FIG. 2. As a result, the noises of the motor can be decreased. Such method can effectively decrease the noises of the motor; however, it is troublesome in implementation. For example, in FIG. 2, when the differential magnetic pole sensing signals H+, H− approach a zero-crossing point, the Hall sensor 100 senses weaker magnetic intensity. Therefore, in practical circuits, sensitivity must be accordingly upgraded to prevent external or internal interference from affecting waveforms of the voltages OUT1, OUT2. In such a situation, when the driving circuit 10 is realized by a single chip, the Hall sensor 100 must be implemented through external connection and different manufacturing processes, to upgrade the sensitivity. As a result, manufacturing cost thereof accordingly increases.